Protein detection and quantitation are important bioanalytical tools. Amounts of proteins in solutions, gels, etc. are determined by their interaction with compounds that are fluorescent dyes. Examples include Albumin-Blue which is based on a cyanin structure (Wolfbeis et al., U.S. Pat. No. 5,182,214), merocyanines (Haugland et al., U.S. Pat. No. 5,616,502), and SYPRO Ruby which is derived from a metal-ligand complex (Haugland et al., Handbook of Fluorescent Probes and Research Products, 9th Edition, also http://www.probes.com). The adsorption of the compounds to the surface of proteins leads, among other effects, to rigidization of the molecular structure of the chromophore, resulting in a drastic increase of the quantum yield. Hydrogen bond formation and shielding against dissolved oxygen quenching of the emission also increase the emission signal.
Czerney et al. (e.g., EP 1318177, EP 1535969, US 2004/260093, DE 10159078) have described reactive labels, inter alia, on the basis of coumarin- and chinolone-based dyes which are suited for the covalent labelling of biomolecules. One example is 4-hydroxysubstituted coumarin dyes, which bear a reactive function.
Other dyes and properties are desirable